You will find that most anything new is much to wide to look right under a narrow old truck.
Although if you don't need a heavy duty truck, the s-10 frame swap seems to be popular, and narrow enough.
Personally I like to use the original frame when updating an old truck. I think it makes a much nicer looking and more professional looking end product. From what I have seen, any kind of new frame under an old truck looks out of place, I don't like that.
My approach is to use the old frame then find a front axle with the brakes you want and then narrow it. Heavy duty rear axles can be found narrow enough.
Check out what I have done to update my AD Chevy truck in the links below.
Grigg
